in a reflex action, muscles respond by doing what?

In a reflex action, the muscles respond by contracting automatically in response to a stimulus.

Quick Scoop: What muscles do in a reflex

When a reflex action happens (like the knee-jerk or pulling your hand away from something sharp), the pathway from the sensory neuron to the spinal cord and back to the motor neuron makes the skeletal muscles contract without waiting for conscious control from the brain. This rapid contraction helps protect the body from damage, for example by tightening a stretched muscle or moving a limb away from danger.

More specifically, in common spinal reflexes:

• The agonist muscle contracts (for example, the quadriceps in the knee-jerk reflex).

• The antagonist muscle relaxes at the same time, so the movement can occur smoothly and quickly.

So, answering the question directly:

In a reflex action, muscles respond by contracting (often with simultaneous relaxation of the opposing muscles) to produce a quick, automatic movement.

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